HP pavilion 705 won't turn on. PLEASE help?

I'll try to be as specific as possible. I have built and repaired computers for years, but this one I can't figure out. The computer was on, and when I woke up it was off. The power button does not light up when pressed. I opened the case. There is a green light on the power supply next to the fan. This light is on and when I press the power button it turns off. Holding the power button in for about five seconds seems to reset the power supply and I can do it again. I have unhooked everything so it's only powersupply and motherboard. There is memory and a chip. There are two fans inside that are powered from connections to the mother board. When the power button is pressed the fans turn around about one full turn then stop. There is a four prong yellow chord going from the power supply to the mother board that I'm not familiar with. When I unhook this chord the fans turn on and spin fine as if the computer is turned on, but nothing else happens. Reconnecting turns off pc

HP pavilion 705 won't turn on. PLEASE help?network security

Your power supply is toast! The four pin yellow cable from power supply to motherboard is the cpu,(processor), power! When the cpu power cable is un-hooked, the cooling fans have enough power to spin. When the cpu's,( which uses a lot of power), power cable is plugged back in, it drains the power supply, so that even with the tiny power usage of the system fan, and processor fan, they no longer spin. No big mystery! How did the power supply just go out, all at once? The capacitors in it are weak, and possibly some are dead. They just had enough electrolytic paste in them to keep them going, until you shut the computer down, this one last time. Have access to another power supply? Put it in, and test my theory! I am sure of this!